I've been growing without an EC meter... even in hydro... I took my source water to the hydro shop for a test to make sure it's not all hard and nasty, it's fine; now I go by the way the plants look.
Scorch? Flush the soil ones, back off on the nutes on the hydro ones.
Hungry? Feed em!
I'll be getting an EC meter for my hydro experiments when I have the cash, but for now everyone is doing aight. It's a necessity in hydro when you are dialing in the nutes for max yield.